Pneumatic shutter mechanism



Jan. 29, 1935. u. M. SCHMIDT PNEUMATIC SHUTTER MECHANISM Filed June 16, 1932 SHUTTER am V gmenkw Patented Jan. 29, 1935 PNEUMATIC SHUTTER MECHANISM Ulrich M. Schmidt, Saginaw, Mich., assignor of one-fourth to George C. Willcox, Saginaw,

Mich.

Application June 16, 1932, Serial No. 617,495

3 Claims.

This. invention relates to pneumatic actuating mechanisms for camera shutters and the like. The bulb and tube customarily used have the disadvantage that upon the release of the bulb after an exposure the shutter closes slowly instead of snapping shut rapidly as is necessary to producethe best pictures. This difiiculty is due principally to the compression of the relatively large volume of air contained in the bulb and the tube leading to the shutter-actuating pump. When the shutter is squeezed the enclosed air must be compressed before it can actuate the piston of the shutter pump. A time lag is thus introduced in the operation of the shutter which naturally tends to slow down the opening of the shutter. This lag is of no practical importance, however, because the strength of the photographers hand is sufiicient to overcome the resistance of the bulb and compress the air quickly enough to open the shutter sufiiciently rapidly for satisfactory results. When the bulb is released, however, the resilience of the bulb unaided must perform the task of closing the shutter. The time lag then occurring results in a harmful slowing down of the closing action of the shutter. The first, and most powerful, part of the bulbs return to its normal shape merely permits the compressed air to expand. Only when the air has expanded can the suction necessary to actuate the shutter pump be created. Only the final expansion of the bulb is effective to create this suction. Since the bulb is only slightly distorted when the shutter starts to close, the force exerted by it is relatively weak. Therefore, the final return of the bulb to normal is slow, since it is opposed by the inertia of the shutter mechanism, and the shutter leaves move slowly across the lens aperture instead of nearly instantaneously, as is necessary to provide the fullest exposure in the shortest possible time.

The object of my invention is to overcome this difficulty and insure a quick closing action of the shutter. I accomplish this by making virtually the entire expansion of the released bulb effective in creating a strong vacuum to actuate the shutter pump promptly and rapidly.

The invention consists in providing a check valve in the enclosed air system of the bulb, tube, and shutter pump, which vents the compressed air slowly out of the system during the exposure, and then closes promptly when the bulb is released so that a suction is created almost at the start of its expansion. The check valve venting orifice is small enough so that during the squeezing of the bulb little air is lost and the opening action of the shutter is slowed down only to a negligible extent.

A preferred form of my device is shown in the drawing, of which Fig. 1 is a diagrammatic view partly in section, showing the device applied to the bulb of a pneumatic shutter mechanism. Fig. 2 shows an application of the device to the tube connecting the bulb and shutter pump, and Fig. 3 shows it incorporated in the piston of the shutter pump.

Fig. 1 shows diagrammatically a shutter of the conventional type in which the shutter leaves are mounted with their centers of gravity above their pivots so that by their weight they remain either open or closed. A bulb 1 is connected to the shutter pump by a tube 2. The bulb may be of the usual type, as shown, or may be replaced by a mechanical bulb, consisting of a cylinder and a spring-returned piston. The novel check valve of the invention is in the form of a tapered plug 3 inserted in the end of the bulb, in the place of the usual stopper or rivet. A hole 4 is drilled lengthwise through the plug from the inner end to communicate with an enlarged bore 5. Bore 5 is formed with a conical ball-seat 6 where it meets the hole 4. The ball 7 is yieldingly held against ball-seat 6 by a spring 8, to close off the hole and prevent the entrance of air into the bulb. A threaded plug 9 is tapped into the outer end of the bore 5, serving to retain the spring 8 in the bore. A small orifice 10 in the plug 9 permits the passage of air into the bore 5 of plug 3. One or both of the holes 4 and 10 is restricted in size to permit theescape during a normal exposure of a substantial portion of the air compressed within the bulb and tube without letting the air escape so rapidly when the bulb is initially squeezed as to slow down the opening of the shutter materially.

Fig. 2 shows the check valve applied to a section of tube 11 adapted to be inserted in the tube 2 between the bulb and the shutter pump. The body 3a of the valve projects laterally from tube 11, with which it can be integral. The operating structure is similar to that of the valve shown in Fig. 1. The body 3a is provided with a hole 4a connecting the tube 11 with an enlarged bore 5a, a conical ball-seat 6a, a ball 7a, a spring 8a to hold the ball in the seat, and a plug 9a tapped into the bore 5a and provided with an air venting orifice 10a.

The check valve shown in Fig. 3 is formed as a part of the piston 12. A hole 4b is drilled longitudinally through the piston, communicating with the interior of the shutter pump cylinder 13. A large bore 51) is drilled in the outer end of the piston, and at its juncture with hole 42; it is shaped to provide a conical ball seat 6b. A ball 7b, a spring 8b, and a threaded plug 1% having a venting orifice 101) are provided exactly as in the other two forms of the device.

The operation of all three devices is the same. Referring to Fig. 1, when the bulb is squeezed to open the shutter, compressing the air in the bulb, the ball 7 is forced away from its seat 6, and air passes through the venting holes 4 and out of the bulb rapidly enough to relieve the pressure within the bulb, tube, and shutter pump during the exposure, but not so rapidly as to impair the initial compression which actuates.

the pump and opens the shutter. At, the end of the exposure the bulb is released, and the ball '7 at once seats tightly, on the ball seat 6, preventing the entrance of any air. Since the pressure within the bulb has been reduced during the exposure Virtually to that of the atmosphere, the initial expansion of the bulb at once sets up a strong suction Which actuates the shutter pump and quickly snaps the shutter closed.

My invention thus for the first time makes effective the first most powerful reaction force of the bulb to produce the desired quick closing of the shutter, whereas only the final weak recovery of the bulb from a slightly compressed position has been available heretofore to actuate the shutter pump, resulting in theslow closing of the shutter, which is undesirable for'the reason given above.

While the form of the invention shown and described is preferred, the scope of the claims is not to be confined to the specific construction squeezed to compress the air within the system to open the shutter and when released to create a suction by its reaction to close the shutter, in combination a check valve communicating with the interior of said system adapted to permit the passage of air out of the system during an exposure and to prevent the entrance of air into the system when the bulb is released.

2. A check valve for use with a pneumatic bulb for actuating a camera shutter, comprising in combination a plug adapted to be inserted in the end of said bulb, provided with an air Venting orifice and valve means within said plug to permit air to pass out of the bulb'and prevent the entranceof air into the bulb.

3. In a pneumatic actuating system for camera shutters, including a resilient bulb adapted when squeezed to compress the air within the system to open the shutter and when released to create a suction to close the shutter, in combination, venting means communicating with the interior of said system adapted to permit the passage of air out of the system and to prevent the inward passage of air.

ULRICH M. SCHMIDT. 

